As a refrigerant compressor used in a vapor compression refrigeration cycle apparatus (a heat pump apparatus or a refrigeration cycle apparatus), a refrigerant compressor has hitherto been used in which the rotating force of a motor is transmitted to a compression mechanism via a drive shaft so as to compress a refrigerant gas. In such a refrigerant compressor, the refrigerant gas compressed by the compression mechanism is discharged into a sealed container, moves through a motor gas flow passage from a lower space to an upper space with respect to the motor, and is then discharged to a refrigerant circuit outside the sealed container. At this time, lubricant oil supplied to the compression mechanism is discharged out of the sealed container while mixing with the refrigerant gas. Conventionally, when the amount of discharged oil to be carried to the refrigerant circuit increases, the performance of a heat exchanger deteriorates, or when the amount of oil stored in the sealed container decreases, compressor efficiency is reduced due to an increase in leakage of the compressed gas. Further, the reliability deteriorates due to lubrication failure of the compressor.
In recent years, size reduction of refrigerant compressors and conversion of the refrigerant used to an alternative refrigerant with little environment load (including natural refrigerants) have accelerated, and there has been a demand to sophisticate the technique of oil separation in the sealed container. On the other hand, the flow states of the refrigerant and lubricant oil during high-speed rotation of the motor in the sealed container and the mechanism of oil separation are considerably complicated, and it is not easy to make an experiment for observing the high-pressure interior of the sealed container. Hence, there are many unidentified details and many unsolved technical problems.
In a high-pressure shell scroll compressor described in Patent Literature 1, a refrigerant drawn by suction by a compression mechanism disposed in the inner upper part of a sealed container is compressed, is temporarily lowered to an oil reservoir at the bottom of the sealed container, and is then lifted from a lower space to an upper space with respect to a motor through a motor gas flow passage, and a high-pressure gas is discharged from a compressor discharge pipe. The high-pressure shell scroll compressor described in Patent Literature 1 includes a fan provided above a motor rotor, and partition plates attached to a motor stator and the motor rotor. The refrigerant and lubricant oil are separated by the centrifugal force generated upon rotation of the fan, and the pressure resistance of the flow in a gap between the partition plates. This prevents the lubricant oil remaining to be separated from the refrigerant from directly flowing into the discharge pipe, that is, prevents the lubricant oil from flowing out of the sealed container.
Patent Literature 2 discloses an oil separation device for a sealed electric compressor including an electrically driven element stored in the inner upper part of a sealed container, a compression element to be driven by the electrically driven element, an oil separation plate opposed to an upper end ring of a rotor of the electrically driven element with a predetermined space between them, and stirring vanes planted on the oil separation plate. In the sealed electric compressor, the stirring vanes are planted only on the lower surface of the oil separation plate.
The effect of the oil separation devices disclosed in Patent Literatures 1 and 2 (the fan and the partition plates in Patent Literature 1, and the oil separation plate and the stirring vanes in Patent Literature 2) for improving the oil separation state in the compressor sealed container is confirmed generally.
Further, it has recently become possible to visualize the flow states of the refrigerant and lubricant oil in the compressor sealed container by utilizing the three-dimensional fluid simulation technique that has made remarkable advance, and new findings have been obtained. For example, Patent Literature 3 discloses a refrigerant compressor in which, by utilizing an increase in head pressure occurring near a leading end portion, in the rotational direction, of an upper balance weight fixed to the upper end of a rotor in a motor provided in a sealed container, an oil return flow passage is formed from the portion near the leading end portion toward the lower end, and high-concentration lubricant oil exposed around the rotor is returned to the lower side of the motor to prevent oil loss.
Usually, a rotor of a DC brushless motor used in the existing compressor has a structure shaped like a circular cylinder in which circular steel sheets are stacked and the upper and lower surfaces of the stack are clamped between metal flat plates. An upper balance weight is accessorily provided on the upper side of an upper end of the rotor, and a lower balance weight is accessorily provided on the lower end of the rotor.